Reduced pressure drop cold plate transition

ABSTRACT

A cold plate apparatus that has an outlet plenum leading to an outlet opening includes an outlet transition that connects the outlet opening to the outlet plenum. The outlet transition defines a smoothly curving flow path from a direction along a long dimension of the outlet plenum, which is parallel to a plane defined by the outlet opening, to a direction along a centerline of the outlet opening, which is at an angle from the plane defined by the outlet opening. The outlet transition provides a smooth variation of cross-sectional area from the outlet plenum to the outlet opening.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.17/134,387 filed Dec. 26, 2020, the complete disclosure of which isexpressly incorporated herein by reference in its entirety for allpurposes.

BACKGROUND

The present invention relates to the electrical, electronic, thermal,mechanical, and computer arts, and more specifically, to apparatus forcooling computer components.

One type of apparatus for cooling computer components is the “coldplate,” which is a conductive heat sink placed in contact with acomponent either directly or with intervening thermal interface material(TIM). A cold plate can be a solid block of metal, often with fins forenhanced air cooling; or it can be a hollow structure through which acoolant (e.g., water) flows from an inlet to an outlet. Such a hollowstructure would include an active volume, often housing a set of fins,where the heat transfer from the component being cooled to the coolantoccurs.

Often, coolant is introduced to and removed from a hollow cold plate vianozzles or fittings that protrude from the cold plate at an angle from(e.g., perpendicular to) the velocity of the coolant through theinterior volume of the cold plate. Transition volumes that connect thenozzle flow to the generally perpendicular direction of interior volumeflow often present turbulent or recirculating pressure drops that reduceflow or require increased pump capacity in the system. Accordingly,there is a need to improve flow behavior in the transition volumes.

SUMMARY

Principles of the invention provide techniques for tuning cold plateplenum transitions.

According to one aspect of this disclosure, an exemplary cold plateapparatus comprises walls that enclose an interior volume that includesan inlet plenum, an outlet plenum, and an active volume fluidlyconnecting the inlet plenum to the outlet plenum. The walls define aninlet opening into the inlet plenum and an outlet opening from theoutlet plenum. The walls define an outlet transition that connects theoutlet plenum to the outlet opening. The outlet transition defines asmoothly curving flow path from a direction along a long dimension ofthe outlet plenum, which is parallel to a plane defined by the outletopening, to a direction along a centerline of the outlet opening, whichis at an angle from the plane defined by the outlet opening. The outlettransition provides a smooth variation of cross-sectional area from theoutlet plenum to the outlet opening.

According to another aspect, an exemplary cold plate apparatus comprisesa top plate that has an inlet opening and an outlet opening through it;a bottom plate; and a plurality of intermediate plates sandwichedbetween the top and bottom plates and attached to each other and to thetop and bottom plates. Each intermediate plate has a cutout, and thecutouts of the plurality of intermediate plates overlap to define aninterior volume enclosed by the top plate, the bottom plate, and theintermediate plates. The interior volume includes an active volume, aninlet plenum at one side of the active volume, an outlet plenum atanother side of the active volume opposite the inlet plenum, an inlettransition at an end of the inlet plenum overlapping the inlet opening,and an outlet transition at an end of the outlet plenum overlapping theoutlet opening. Inward edges of the cutouts of the intermediate platesare staggered so that the outlet transition defines a curving flow pathfrom a direction along a long dimension of the outlet plenum, which isparallel to a plane defined by the outlet opening, to a direction alonga centerline of the outlet opening, which is at an angle from the planedefined by the outlet opening.

According to still another aspect, an exemplary method of making a coldplate apparatus comprises obtaining a plurality of plates; defining aninlet plenum, an active volume, an outlet plenum, an outlet opening, andan outlet transition connecting the outlet plenum to the outlet opening,by shaping a cutout in each plate and stacking the plurality of platestogether in an assembly according to a final cold plate design; andbonding the plurality of plates together in the assembly. The outlettransition defines a smoothly curving flow path from a direction along along dimension of the outlet plenum, which is parallel to a planedefined by the outlet opening, to a direction along a centerline of theoutlet opening, which is at an angle from the plane defined by theoutlet opening.

According to yet another aspect, an exemplary method of directingcoolant through a cold plate apparatus comprises redirecting the coolantfrom an outlet plenum bulk velocity of flow along a length of an outletplenum to an outlet opening bulk velocity of flow, at an angle from theoutlet plenum bulk velocity, through an outlet opening that is connectedin fluid communication with the outlet plenum; and releasing the coolantthrough the outlet opening. Redirecting the coolant from the outletplenum bulk velocity to the outlet opening bulk velocity includessmoothly turning the direction of the coolant from the outlet plenumbulk velocity to the outlet opening bulk velocity, without significantrecirculation or turbulence, inside an outlet transition structureformed in the cold plate and connecting the outlet plenum in fluidcommunication with the outlet opening, without significant recirculationor turbulence.

According to a further aspect, an exemplary apparatus comprises anelectronic component that dissipates heat; a cold plate apparatusattached in thermal connection to the electronic component; and a pumpthat forces a liquid coolant through the cold plate apparatus. The coldplate apparatus comprises: a bottom portion surrounding an interiorvolume; and a top portion attached to the bottom portion and enclosingthe interior volume. The top portion includes an outlet opening into theinterior volume. The interior volume includes an outlet transition thatconnects the outlet opening to an outlet plenum. The outlet transitiondefines a smoothly curving flow path from a direction along a longdimension of the outlet plenum, which is parallel to a plane defined bythe outlet opening, to a direction along a centerline of the outletopening, which is at an angle from the plane defined by the outletopening.

In view of the foregoing, techniques of the present invention canprovide substantial beneficial technical effects. For example, one ormore embodiments provide one or more of:

Enhanced flow profile through an active volume of the cold plate.

Reduced pressure drop at inlet and outlet of the cold plate.

Enhanced heat transfer within an active volume of the cold plate.

These and other features and advantages of the present invention willbecome apparent from the following detailed description of illustrativeembodiments thereof, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an exterior view of a conventional cold plate.

FIG. 2 depicts a top cutaway view of the cold plate of FIG. 1 , showinga conventional transition from outlet plenum to outlet nozzle.

FIG. 3 depicts a top cutaway view of a cold plate with a reducedpressure drop outlet transition according to an exemplary embodiment.

FIG. 4 depicts a detail view of the cold plate shown in FIG. 3 .

FIG. 5 depicts a side cutaway view of an outlet transition of the coldplate shown in FIG. 3 .

FIG. 6 depicts certain dimensions of the outlet transition shown in FIG.5 .

FIG. 7 depicts certain dimensions of the outlet transition shown in FIG.5 .

FIG. 8 depicts a side cutaway view of an inlet transition of the coldplate shown in FIG. 3 .

FIG. 9 depicts in a flowchart steps of a method for making a cold plateapparatus, according to an exemplary embodiment.

FIG. 10 depicts in a flowchart steps of a method for modifying coolantflow through a cold plate apparatus, according to an exemplaryembodiment.

FIG. 11 depicts in a schematic an apparatus including an electroniccomponent, a cold plate, and a pump, according to an exemplaryembodiment.

DETAILED DESCRIPTION

A cold plate is a familiar structure in the field of semiconductordevice cooling. A cold plate typically directs an incompressible fluid(e.g., liquid) flowing through a somewhat tortuous path to accomplishheat transfer from a semiconductor device through the structure of thecold plate into the fluid.

FIG. 1 depicts a cold plate 100 with a top plate 101, an inlet nozzle102, and an outlet nozzle 104. FIG. 2 depicts a cutaway view of the coldplate 100. FIG. 2 shows a conventional outlet transition 106, an outletopening 108, an outlet plenum 114, an inlet plenum 116, and an activevolume 118. Flow through the cold plate 100 goes from the inlet nozzle102 through the inlet plenum 116 and the active volume 118 to the outletplenum 114, then through the outlet transition 106 and the outletopening 108 to the outlet nozzle 104.

Notably, the conventional outlet transition 106 is a “hard” transition,that is it lacks any kind of structure to redirect flow from a directionalong the outlet plenum 114 to a perpendicular direction through theoutlet opening 108. As a result, flow from the outlet plenum 114 to theoutlet nozzle 104 can become very turbulent and may generate significantrecirculation as it abruptly changes direction by ninety degrees underthe outlet opening 108. The turbulence and recirculation introducesignificant pressure loss, which slows down the flow through the activevolume 118 (i.e., for a fixed supply pressure the volumetric flow willbe lower due to this undesirable pressure loss from turbulence, or ahigher supply pressure will be needed to obtain the desired volumetricflow rate). The reduced volumetric flow rate due to pressure drop at theoutlet transition 106 detracts from heat transfer in the active volume118. Not only is there less coolant flowing through the active volume,but additionally the slower flow results in a lower heat transfer at theinterface between the coolant and cold plate. Therefore, heat transferin the active volume 118 with the conventional outlet transition 106 issignificantly less than it could be if there was a reduced pressure dropbetween the outlet plenum 114 and the outlet opening 108 for a givenavailable system pressure drop.

In view of this understanding, one or more embodiments advantageouslyprovide a smooth transition from outlet plenum to outlet opening and/orfrom inlet opening to inlet plenum, with a reduced pressure drop, whichin turn enhances coolant flow rate and heat transfer in the activevolume for the same supply pressure. In this regard, FIG. 3 depicts atop cutaway view of a cold plate 200 with a reduced pressure drop outlettransition 206 according to an exemplary embodiment. The exemplary coldplate 200 has a top plate 201, an inlet nozzle 202, and an outlet nozzle204 (not shown in FIG. 3 , but attached at an outlet opening 208 andshown in FIG. 5 ). The top plate 201 covers an outlet plenum 214, aninlet plenum 216, and an active volume 218. In one or more embodiments,the active volume 218 includes an extended surface for enhanced heattransfer (e.g., fins, pins, or mesh surface that establishes channelsfluidly connecting the inlet plenum 216 to the outlet plenum 214). Inone or more embodiments, the top plate 201 has a cutout matching anouter diameter of the outlet nozzle 204. A centerline of the outletnozzle 204 extends at an angle (e.g., in one or more embodiments greaterthan 50°; in other embodiments, greater than 70°; in other embodiments,greater than 85°) from a length of the outlet plenum 214. The outlettransition 206 connects the outlet plenum 214 in fluid communicationwith the outlet opening 208. In one or more embodiments, the outletopening 208 is formed in a topmost intermediate plate 222 (as shown inFIG. 6 , immediately underlying the top plate 201) and matches an innerdiameter of the outlet nozzle 204. In one or more embodiments, as shownin FIG. 8 , a similar reduced pressure drop inlet transition 207 may beprovided to connect the inlet nozzle 202 and the inlet opening 209 withthe inlet plenum 216.

Referring also to FIGS. 4 and 8 , in one or more embodiments theinventive cold plate 200 is laminated, that is, built as a stack ofplates fastened together; e.g., the top plate 201 (see FIG. 3 ), abottom plate 203, and intermediate plates such as 210 and 212. Thus, aplurality of intermediate plates 210, 212 are sandwiched between the topand bottom plates 201, 203 and are attached to each other and to the topand bottom plates. For example, the plates may be attached together bydiffusion bonds or by thermal compression bonds. In other embodiments,the cold plate 200 is fabricated from two cast or machined pieces (thetop “plate” 201 and the bottom “plate” 203) or is made in a single pieceby additive manufacturing (e.g., 3-D printing). The bonds between platesare coolant (e.g., water) tight. Each intermediate plate has a cutout,e.g., 211, and the cutouts of the plurality of intermediate platesoverlap to define an interior volume that is enclosed by the top plate,the bottom plate, and the intermediate plates. The interior volumeincludes the active volume 218, the inlet plenum 216 at one side of theactive volume, the outlet plenum 214 at another side of the activevolume opposite the inlet plenum, the inlet transition 207 at an end ofthe inlet plenum that overlaps the inlet opening, and the outlettransition 206 at an end of the outlet plenum 214 that overlaps theoutlet opening 208. In one or more embodiments, the inlet opening 209and inlet transition 207 are symmetric to the outlet opening 208 andoutlet transition 206.

In one or more embodiments, the first end of the outlet transition 206is underneath a footprint of the outlet opening 208 projected into theinterior volume of the apparatus and is offset from the centerline ofthe outlet opening toward the outlet plenum. Advantageously, thetransition 206 is structured to eliminate blind ends extending beyondthe outlet opening 208. In one or more embodiments, as shown in FIG. 6 ,the transition begins at a distance D before an edge 213 of the outletopening 208 that is distal from the plenum 214. For example, thetransition may begin at a point that is offset from the distal edge 213of the outlet opening 208 by at least 10% of the outlet openingdiameter. In one or more embodiments, the distance D is on the order ofone half of the outlet diameter from the distal edge of the outletopening 208 footprint. The beginning 224 of the transition 206 is chosento maintain a substantially constant or smoothly varying cross-sectionof flow as the transition turns the flow from a direction along thelength of the plenum 214 to a direction through the outlet opening at anangle (e.g., in one or more embodiments greater than 50°; in otherembodiments, greater than 70°; in other embodiments, greater than 85°)from the length of the plenum 214. If the plenum 214 has a largercross-section than the outlet opening 208 cross-section, then thetransition begins further from the distal edge 213 of the outletopening, i.e., the distance D would be further into the plenum 214 thanone-half the diameter of the outlet opening 208. For example, inconnecting a larger plenum cross-section to a smaller outlet openingcross-section, the transition starts further into the plenum as part ofa smooth variation of cross-section.

In one or more embodiments, a smooth variation of cross-sectional areais one for which computational fluid dynamics (CFD) analysis, performedusing ANSYS® or other CFD software, indicates no significantrecirculation or turbulence of flow in the transition. (ANSYS is aregistered trademark of ANSYS, INC. of Canonsburg, Pennsylvania.) In oneor more embodiments, “significant” recirculation or turbulence isrecirculation or turbulence that contributes more than 5% of the overallpressure drop through the transition volume. In one or more embodiments,the CFD mesh size is reduced (i.e., more, smaller elements) untilmaximum and minimum velocity values obtained with a smaller (“optimum”)mesh size remain within 5% of values obtained with a next larger meshsize. In one or more embodiments, the CFD analysis is performed for thedesign coolant (e.g., water, glycol, mixtures thereof) at a range ofdesign mass or volumetric flow rates and temperatures.

In one or more embodiments, a “planar” cross-section of the outlettransition 206, taken at each intermediate plate parallel to the surfaceof the plenum opposite the outlet opening, varies in radius R from thelowest intermediate plate 220 toward the topmost intermediate plate 222.

In one or more embodiments, the planar cross-section of the outlettransition diminishes in radius from the lowest intermediate platetoward the topmost intermediate plate. In other words, as shown in FIG.7 , where each layer of intermediate plate is a layer i=1 . . . N frombottom to top, the radius R_(i) at layer i diminishes as i increases.For example, in one or more embodiments wherein the radius of the outletopening 208 is less than one half the width of the outlet plenum 214, atthe lowest intermediate plate 220 the radius R_(i) of the outlettransition is at least one half the width W of the plenum. Then at theintermediate plate 222 adjacent to the outlet opening, the radius RN ofthe outlet transition is equal to the radius of the outlet opening. Inone or more embodiments, the cross-section of the outlet transition 206,taken at each intermediate plate perpendicular to the centerline of theoutlet opening 208, shifts its center toward the centerline of theoutlet opening from the lowest intermediate plate 220 toward the topmostintermediate plate 222. In one or more embodiments, an edge of thecross-section of the outlet transition 206 shifts toward the distal edge213 of the outlet opening 208, along the long direction of the outletplenum 214, from the lowest intermediate plate 220 toward the topmostintermediate plate 222.

Additionally, the transition provides a smoothly diminishing radius ofcurvature C for turning the flow. For example, a radius of curvature C₁from the transition flow centerline to the lowest intermediate plate 220is greater than a radius of curvature CN from the transition flowcenterline to the topmost intermediate plate 222. A smooth change inradius of curvature is beneficial for reduced pressure drop. In one ormore embodiments, the radius of curvature C (shown in FIG. 6 ) of thetransition 206 is at least equal to one half the width W (shown in FIG.7 ) of the outlet plenum at the beginning of the transition and is atleast equal to the radius RN (shown in FIG. 7 ) of the outlet opening atthe end of the transition. In one or more embodiments, the radius ofcurvature C_(i) of the transition is approximately equal to the radiusR_(i) of the cross-section of the transition at each point along thetransition. Generally, a smooth change in radius of curvature is suchthat CFD analysis, as discussed above, shows smoothly turning flow,i.e., monotonically changing flow vectors without significantrecirculation or turbulence.

Thus, in one or more embodiments, the outlet transition 206 is shaped toprovide a smooth (generally non-turbulent, non-recirculating) change indirection of the coolant flowing from the outlet plenum 214 through theoutlet opening 208 into an outlet nozzle 204. In other words, the outlettransition 206 is coextensive with the outlet plenum 214 at a first endand coextensive with the outlet opening 208 at a second end, and thefirst end of the outlet transition 206 is offset from the centerline ofthe outlet opening 208 along the long direction of the outlet plenum, sothat the outlet transition 206 defines a smoothly curving flow path froma direction along a long dimension of the outlet plenum 214, which isparallel to a plane defined by the outlet opening 208, to a directionalong a centerline of the outlet opening 208, which is at an angle from(e.g., in one or more embodiments greater than 50°; in otherembodiments, greater than 70°; in other embodiments, greater than 85°)the plane defined by the outlet opening. In one or more embodiments, asmoothly curving surface for the outlet transition 206 can beconstructed from a stack of N+1 layered intermediate plates 210, 212,220, 222 by staggering inward edges of the plates so that a distanceD_(i) from an inward edge of each plate i to the inner edge 213 of theoutlet opening 208 varies according to D_(i)=D_(i) (1−(i−1)/N). In anon-limiting example, the smoothly curving surface can be formed from anumber of small, discrete steps corresponding, for example, to theplates used to build up the cold plate. In a non-limiting example, thereare at least five such steps between the top and bottom plates,sequentially recessed as shown in FIG. 6 .

Thus, FIG. 9 depicts a method 600 of making a cold plate apparatus,according to an exemplary embodiment. The method 600 includes at 602forming an interior volume by stacking and attaching together aplurality of intermediate plates 210, 212 with cutouts of theintermediate plates aligned to each other. The interior volume includesan active volume 218, an inlet plenum 216 at one side of the activevolume, an outlet plenum 214 at another side of the active volumeopposite the inlet plenum, an inlet transition 207 (shown in FIG. 8 ) atan end of the inlet plenum, and an outlet transition 206 at an end ofthe outlet plenum. The method 600 also includes at 604 enclosing theinterior volume by attaching top and bottom plates 201, 203 thatsandwich the plurality of intermediate plates, with an inlet opening 209of the top plate overlapping the inlet transition 207 of the interiorvolume and with an outlet opening 208 of the top plate overlapping theoutlet transition 206 of the interior volume. The method also includesat 606 shaping the outlet transition to define a curving flow path froma direction along a long dimension of the outlet plenum, which isparallel to a plane defined by the outlet opening, to a direction alonga centerline of the outlet opening, which is at an angle from (e.g., inone or more embodiments greater than 50°; in other embodiments, greaterthan 70°; in other embodiments, greater than 85°) the plane defined bythe outlet opening. Steps of the method can be done in other orders,i.e., step 606 can be performed as part of step 602 and/or before step604 (for example, by assembling pre-profiled sheets). For example, inone or more embodiments, the interior volume including the outlettransition can be formed by milling a billet stock; then the top platecan be attached. In one or more embodiments, the entire cold plate canbe formed by additive manufacturing such as three-dimensional (3D)printing.

According to another aspect, FIG. 10 depicts a method 700 of directingcoolant through a cold plate apparatus. The method 700 includes at 702receiving the coolant through an inlet opening at an inlet pressure withan inlet opening bulk velocity along a centerline of the inlet opening.At 704 the method includes initially redirecting the coolant from theinlet opening velocity to an inlet plenum bulk velocity at an angle(e.g., in one or more embodiments greater than 50°; in otherembodiments, greater than 70°; in other embodiments, greater than 85°)from the inlet opening velocity and along a length of an inlet plenumthat is connected in fluid communication with the inlet opening. Forexample, in one or more embodiments, initially redirecting the coolantincludes at 706 smoothly turning the direction of the coolant from theinlet opening velocity to the inlet plenum bulk velocity, inside aninlet transition structure formed in the cold plate and connecting theinlet opening in fluid communication with the inlet plenum, such thatgenerally laminar and non-recirculating flow is maintained within theinlet transition structure. Recall that in one or more embodiments ofthe cold plate apparatus 200, an inlet transition is identical orsimilar to the outlet transition 206.

In one or more embodiments, the method 700 also includes at 714redirecting the coolant from the inlet plenum bulk velocity to an activevolume bulk velocity, at an angle (e.g., in one or more embodimentsgreater than 50°; in other embodiments, greater than 70°; in otherembodiments, greater than 85°) from the inlet plenum bulk velocity,through an active volume adjacent to the inlet plenum; and at 716redirecting the coolant from the active volume bulk velocity to anoutlet plenum bulk velocity, at an angle (e.g., in one or moreembodiments greater than 50°; in other embodiments, greater than 70°; inother embodiments, greater than 85°) from the active volume bulkvelocity.

In one or more embodiments, the method 700 also includes at 708 finallyredirecting the coolant from the outlet plenum bulk velocity flow alonga length of an outlet plenum to an outlet opening bulk velocity ofgenerally laminar flow at an angle (e.g., in one or more embodimentsgreater than 50°; in other embodiments, greater than 70°; in otherembodiments, greater than 85°) from the outlet plenum bulk velocitythrough an outlet opening that is connected in fluid communication withthe outlet plenum; and at 710 releasing the coolant through the outletopening. In one or more embodiments, finally redirecting the coolantincludes at 712 smoothly turning the direction of the coolant from theoutlet plenum bulk velocity to the outlet opening bulk velocity, insidean outlet transition structure formed in the cold plate and connectingthe outlet plenum in fluid communication with the outlet opening, suchthat generally laminar flow is established within the outlet transitionstructure.

According to another aspect, as shown in FIG. 11 , in an apparatus 800an electronic component 801 that dissipates heat (e.g., an integratedcircuit chip) is attached to a cold plate apparatus 200 as describedabove. An intermediate thermal interface material (TIM) 802 may beprovided between the electronic component 801 and the cold plateapparatus 200. A pump 804 forces liquid coolant through the cold plate200 in a closed loop heat exchange system with an external heatexchanger 806 (shown) or through an open loop heat exchange system. Inone or more embodiments, the cold plate apparatus 200 and the electroniccomponent 801 are mounted in a cabinet or chassis 808 that constrainsthe piping 810 between pump 804 and cold plate 200 to be at an angle(e.g., in one or more embodiments greater than 50°; in otherembodiments, greater than 70°; in other embodiments, greater than 85°)from the cold plate, substantially as shown.

Given the preceding description and the accompanying drawings, anordinary skilled worker will appreciate that according to one aspect ofthis disclosure, an exemplary cold plate apparatus 200 comprises walls201, 203 that enclose an interior volume that includes an inlet plenum216, an outlet plenum 214, and an active volume 218 fluidly connectingthe inlet plenum to the outlet plenum. The walls define an inlet opening209 into the inlet plenum and an outlet opening 208 from the outletplenum. The walls define an outlet transition 206 that connects theoutlet plenum to the outlet opening. The outlet transition 206 defines asmoothly curving flow path from a direction along a long dimension ofthe outlet plenum, which is parallel to a plane defined by the outletopening, to a direction along a centerline of the outlet opening, whichis at an angle from the plane defined by the outlet opening. The outlettransition provides a smooth variation of cross-sectional area from theoutlet plenum to the outlet opening.

In one or more embodiments, the outlet transition is coextensive withthe outlet plenum at a first end and coextensive with the outlet openingat a second end. In one or more embodiments, the first end of the outlettransition is within a footprint of the outlet opening projected intothe interior volume of the apparatus. In one or more embodiments, thefirst end of the outlet transition is offset from the centerline of theoutlet opening toward the outlet plenum. In one or more embodiments,cross-sections of the outlet transition, taken in planes perpendicularto the centerline of the outlet opening, vary in radius from the bottomsurface of the outlet plenum toward the upper surface of the outletplenum. In one or more embodiments, the cross-sections of the outlettransition smoothly diminish in radius from the bottom surface of theoutlet plenum toward the upper surface of the outlet plenum. In one ormore embodiments, cross-sections of the outlet transition, taken inplanes perpendicular to the centerline of the outlet opening, shifttheir centers toward the centerline of the outlet opening from thebottom surface of the outlet plenum toward the upper surface of theoutlet plenum. In one or more embodiments, the cross-sections of theoutlet transition shift their inward edges first toward and then beyondthe centerline of the outlet opening, along the long direction of theoutlet plenum, from the bottom surface of the outlet plenum toward theupper surface of the outlet plenum.

According to another aspect, an exemplary cold plate apparatus 200comprises a top plate 201 that has an inlet opening 209 and an outletopening 208 through it; a bottom plate 203; and a plurality ofintermediate plates 210, 212, 220, 222 that are sandwiched between thetop and bottom plates and attached to each other and to the top andbottom plates. Each intermediate plate has a cutout 211, and the cutoutsof the plurality of intermediate plates overlap to define an interiorvolume enclosed by the top plate, the bottom plate, and the intermediateplates. The interior volume includes an active volume 218, an inletplenum 216 at one side of the active volume, an outlet plenum 214 atanother side of the active volume opposite the inlet plenum, an inlettransition 207 at an end of the inlet plenum overlapping the inletopening, and an outlet transition 206 at an end of the outlet plenumoverlapping the outlet opening. Inward edges of the cutouts of theintermediate plates are staggered so that the outlet transition definesa curving flow path from a direction along a long dimension of theoutlet plenum, which is parallel to a plane defined by the outletopening, to a direction along a centerline of the outlet opening, whichis at an angle from the plane defined by the outlet opening.

In one or more embodiments, cutouts of the intermediate plates arestaggered so that the outlet transition is coextensive with the outletplenum at a first end and coextensive with the outlet opening at asecond end, and the first end of the outlet transition is offset fromthe centerline of the outlet opening along the long direction of theoutlet plenum. In one or more embodiments, the first end of the outlettransition is within a footprint of the outlet opening projected intothe interior volume of the apparatus. In one or more embodiments, thereare N+1 intermediate plates and inward edges of the intermediate platesare staggered so that a distance D_(i) from an outward edge of theoutlet opening to the inward edge of each intermediate plate i variesaccording to D_(i)=D_(i) (1−(i−1)/N). In one or more embodiments,cross-sections of the outlet transition, taken at each intermediateplate perpendicular to the centerline of the outlet opening, vary inradius from the lowest intermediate plate toward the topmostintermediate plate. In one or more embodiments, the cross-sections ofthe outlet transition smoothly diminish in radius from the lowestintermediate plate toward the topmost intermediate plate. In one or moreembodiments, cross-sections of the outlet transition, taken at eachintermediate plate perpendicular to the centerline of the outletopening, shift their centers toward the centerline of the outlet openingfrom the lowest intermediate plate toward the topmost intermediateplate. In one or more embodiments, the cross-sections of the outlettransition shift their inward edges first toward and then beyond thecenterline of the outlet opening, along the long direction of the outletplenum, from the lowest intermediate plate toward the topmostintermediate plate. In one or more embodiments, the inward edges of thecutouts of the intermediate plates are staggered to define an inlettransition similar to the outlet transition.

According to another aspect, an exemplary method 600 of making a coldplate apparatus 200 comprises obtaining a plurality of plates 201, 203,210, 212, 220, 222; defining an inlet plenum 216, an active volume 218,an outlet plenum 214, an outlet opening 208, and an outlet transition206 connecting the outlet plenum to the outlet opening, by shaping acutout 211 in each plate and stacking the plurality of plates togetherin an assembly according to a final cold plate design; and bonding theplurality of plates together in the assembly. The outlet transitiondefines a smoothly curving flow path from a direction along a longdimension of the outlet plenum, which is parallel to a plane defined bythe outlet opening, to a direction along a centerline of the outletopening, which is at an angle from the plane defined by the outletopening. In one or more embodiments, the outlet transition iscoextensive with the outlet plenum at a first end and coextensive withthe outlet opening at a second end. In one or more embodiments, theoutlet transition varies in cross-sectional area from the first end tothe second end.

In one or more embodiments, the method also comprises performingcomputational fluid dynamics analysis of an initial cold plate design,given design values of mass flow rate and fluid properties of a coolantflowing through the outlet transition; identifying significantturbulence or recirculation in the simulation of coolant flow throughthe outlet transition; generating the final cold plate design byadjusting curvature and cross-sectional areas of the outlet transitionuntil computational fluid dynamics analysis indicates no significantturbulence and no significant recirculation at an optimum mesh size.

According to another aspect, an exemplary method 700 of directingcoolant through a cold plate apparatus comprises at 708 redirecting thecoolant from an outlet plenum bulk velocity of flow along a length of anoutlet plenum to an outlet opening bulk velocity of laminar flow, at anangle from the outlet plenum bulk velocity, through an outlet openingthat is connected in fluid communication with the outlet plenum; andreleasing the coolant through the outlet opening. Redirecting thecoolant from the outlet plenum bulk velocity to the outlet opening bulkvelocity includes smoothly turning the direction of the coolant from theoutlet plenum bulk velocity to the outlet opening bulk velocity, withoutsignificant recirculation or turbulence, inside an outlet transitionstructure 206 that is formed in the cold plate and connects the outletplenum in fluid communication with the outlet opening.

According to another aspect, an exemplary apparatus comprises anelectronic component that dissipates heat; a cold plate apparatusattached in thermal connection to the electronic component; and a pumpthat forces a liquid coolant through the cold plate apparatus. The coldplate apparatus comprises: a bottom portion surrounding an interiorvolume; and a top portion attached to the bottom portion and enclosingthe interior volume. The top portion includes an outlet opening into theinterior volume. The interior volume includes an outlet transition thatconnects the outlet opening to an outlet plenum. The outlet transitiondefines a smoothly curving flow path from a direction along a longdimension of the outlet plenum, which is parallel to a plane defined bythe outlet opening, to a direction along a centerline of the outletopening, which is at an angle from the plane defined by the outletopening.

In one or more embodiments, the bottom portion comprises a bottom plateand a plurality of intermediate plates. The plurality of intermediateplates are attached to each other, to the bottom plate, and to the topportion. Cutouts of the plurality of intermediate plates define theinterior volume of the apparatus.

In one or more embodiments, the outlet transition is coextensive withthe outlet plenum and with the outlet opening and smoothly diminishes incross-sectional area from the outlet plenum to the outlet opening.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method of making a cold plate apparatus, themethod comprising: obtaining a plurality of plates; defining an inletplenum, an active volume, an outlet plenum, an outlet opening, and anoutlet transition connecting the outlet plenum to the outlet opening, byshaping a cutout in each plate and stacking the plurality of platestogether in an assembly according to a final cold plate design; andbonding the plurality of plates together in the assembly; wherein theoutlet transition defines a smoothly curving flow path from a directionalong a long dimension of the outlet plenum, which is parallel to aplane defined by the outlet opening, to a direction along a centerlineof the outlet opening, which is at an angle from the plane defined bythe outlet opening.
 2. The method of claim 1 wherein the outlettransition is coextensive with the outlet plenum at a first end andcoextensive with the outlet opening at a second end.
 3. The method ofclaim 1 wherein the outlet transition varies in cross-sectional areafrom the first end to the second end.
 4. The method of claim 3, furthercomprising: performing computational fluid dynamics analysis of aninitial cold plate design, given design values of mass flow rate andfluid properties of a coolant flowing through the outlet transition;identifying turbulence or recirculation in the simulation of coolantflow through the outlet transition; generating the final cold platedesign by adjusting curvature and cross-sectional areas of the outlettransition until computational fluid dynamics analysis indicates noturbulence and no recirculation at an optimum mesh size.
 5. A method ofdirecting coolant through a cold plate apparatus, the method comprising:redirecting the coolant from an outlet plenum bulk velocity of flowalong a length of an outlet plenum to an outlet opening bulk velocity oflaminar flow, at an angle from the outlet plenum bulk velocity, throughan outlet opening that is connected in fluid communication with theoutlet plenum; and releasing the coolant through the outlet opening;wherein redirecting the coolant from the outlet plenum bulk velocity tothe outlet opening bulk velocity includes smoothly turning the directionof the coolant from the outlet plenum bulk velocity to the outletopening bulk velocity, without recirculation or turbulence, inside anoutlet transition structure formed in the cold plate and connecting theoutlet plenum in fluid communication with the outlet opening.